A sensitive magnetic position sensor has been proposed in U.S. Ser. No. 229,396, filed Aug. 8, 1988, now U.S. Pat. No. 4,926,122 assigned to the assignee of this invention, which incorporates a permanent magnet, a flux density sensor mounted on the magnet, and a toothed excitation element movable past the magnet to vary the magnetic flux affecting the flux sensor. To optimize sensitivity, a thin intermediate layer (about 0.1 mm thick) of ferromagnetic material with soft magnetic properties is sandwiched between the magnet and the flux sensor. This enables the flux to more readily shift with respect to the sensor upon movement of the toothed element. It is proposed in that disclosure to provide the soft magnetic layer by securing a foil of such material to the magnet or by adding a layer of iron powder to powdered magnet material and forming both by compressing and/or sintering. It is further proposed that the permanent magnet be made of MQ2 magnet material which is a hot pressed Nd-Fe-B alloy having a high energy product and is a trademarked product of General Motors Corporation.
U.S. Pat. No. 4,792,367 to Lee, also assigned to the assignee of this application, discloses the MQ2 material which is a hot pressed rare earth-iron alloy further including boron. The preferred methods of forming permanent magnets from that material include overquenching a molten mixture of the precursors by melt spinning to obtain an amorphous material having little intrinsic coercivity and then hot pressing to promote crystal growth to the optimum size for the desired hard magnetic properties. (An even higher energy product magnet can be formed by hot pressing and hot working such amorphous material to form a fine deformed grain microstructure consisting predominantly of an Nd.sub.2 Fe.sub.14 B phase and an intergranular phase.) An intrinsic room temperature coercivity exceeding 15 kOe is obtained in the hot pressed only material, along with very high remanence and high energy product. The magnet material, when in the overquenched amorphous condition, exhibits the high magnetic permeability required of the intermediate layer of the sensor.